January 29th, 2003, 03:53 AM
Networking Simplified - Part 05
This is the fifth edition to my series entitled "Networking Simplified."
In this edition, I will go over the OSI model, as promised. The OSI model
will take up the entirity of the tutorial, so keep in note that Networking
Simplified 5 is OSI only for your own personal reference.
First i will begin with simply listing the layers as mentioned in the 4th
Layer 1 - The Physical Layer
Layer 2 - The data-link Layer
Layer 3 - The Network Layer
Layer 4 - The Transport Layer
Layer 5 - The Session Layer
Layer 6 - The Presentation Layer
Layer 7 - The Application Layer
Layer 1 of course, the physical layer, is exactly what it sounds like.
Whether you are speaking in terms of a router, a hub, a switch etc this is
what provides that hardware with the ability to pass and receive the data
on its line. The mechanics and electricty of such provide for this.
Layer 2. This layer is basically what links the hardware's jobs to the
network. It is what allows transmission ports to be able to go. It is
somewhat of a timer theoretically speaking, as it synchronizes data when
linking, hence the name, data-link layer.
Layer 3. The network layer is possibly the most known of layers. Whether
because of its easy to remember name since the term network is so vastly
known, or because it is what handles the packets. The packets are routed
along to the correct destination on the network going outward, while still
receiving the transmissions of packets. The job of this layer is to
forward data and route it.
Layer 4. The transport layer is a simple one in which all it does is
check for errors of packets. If they have arrived, it can forward them
further and along to complete the transfer.
Layer 5. The Session Layer. This is the layer that enables you to talk on
your instant messaging programs, your Internet Relay Chat, your anything
real-time. What it does is allows for dialogs by coordinating the
applications as they go.
Layer 6. The Presentation Layer. This layer is commonly found built-in
operating systems. Commonly called the syntax layer, because of the way it
handles the data presentation. It can send your php code across the
internet and have it bring up an advertisement. It is exactly what it
says, a presentation format that changes presentation of the stream to the
Layer 7. The application layer.. The most "used" so to speak layer by the
end user. It in itself is what provides for user authentication across the
net. It handles encryption, it handles data formats of all shapes and
sizes. Bear in mind that the term "application" does not necessarily mean
a program. It simply means that this is where the finality of all the data
processing finishes, if its desired destination is this far. Communication
works here through a partnership. Sometimes referred to as a hand-shake.
OSI was developed by telecommunication companies in the early eighties.
Finally after years of experimentation and morphing, it became known as
the ISO, or International Organization of Standards. (Not to be confused
with software isos.) Its original intent was just to provide for chosen
interfaces. It transformed into the reference layer and how the internet
This concludes my 5th tutorial, as the OSI model is so vast. I will
include some links below for further reference, as these tutorials cannot
provide for the ability of making a user interaction with pictures and so
http://webtraining.infoworld.com/Catalog/scoc01.htm < - cisco information
http://munshi.sonoma.edu/s96/bus420/osilecture.html < - nice lecture